SharePoint 2013 Branding: Fixed Layout

It's quite easy to create a fixed width design in SharePoint 2013. Just a few lines of code and you're up and running.
We need to start by editing our masterpage.
Wrap all the content inside the #s4-workplace div with a new div: <div class="wrapper"></div>.
The div.wrapper will be only direct descendant of #s4-workplace.
Next we need a bit of CSS.